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<h2><a name="javah">Javah</a></h2>
<h3>Description</h3>
<p>Generates JNI headers from a Java class.</p>
<p> When this task executes, it will generate the C header and source files that
are needed to implement native methods. JNI operates differently depending on
whether <a href="http://docs.oracle.com/javase/7/docs/technotes/tools/windows/javah.html">JDK1.2+</a>
or <a href="http://java.sun.com/products/jdk/1.1/docs/tooldocs/win32/javah.html">pre-JDK1.2</a>
systems are used.</p>

<p>If you are building with Java 8 or above consider
  using <a href="javac.html"><code>javac</code></a>'s <code>nativeheaderdir</code>
  attribute instead which allows you to compile the classes and
  generate the native header files with a single step.</p>

<p><b>Note</b> the <code>javah</code> has been deprecated as of Java 9
  and is scheduled to be removed with Java 10.</p>

<p>It is possible to use different compilers. This can be selected
with the <code>implementation</code> attribute or a nested element.  <a
name="implementationvalues">Here are the choices of the attribute</a>:</p>
<ul>
  <li>default - the default compiler for the platform.</li>
  <li>sun (the standard compiler of the JDK)</li>
  <li>kaffeh (the native standard compiler of <a href="http://www.kaffe.org" target="_top">Kaffe</a>)</li>
  <li>gcjh (the native standard compiler
  of <a href="http://gcc.gnu.org/java/"
        target="_top">gcj and gij</a>) <em>since Apache Ant 1.8.2</em></li>
  <li>forking - runs the javah executable via its command line
    interface in a separate process. Default when not running on
    Kaffee or gcj/gij <em>since Ant 1.9.8</em></li>
</ul>

<p><b>Note:</b> if you are using this task to work on multiple files
  the command line may become too long on some operating systems.
  Unfortunately the javah command doesn't support command argument
  files the way javac (for example) does, so all that can be done is
  breaking the amount of classes to compile into smaller chunks.</p>

<h3>Parameters</h3>
<table border="1" cellpadding="2" cellspacing="0">
  <tr>
    <td valign="top"><b>Attribute</b></td>
    <td valign="top"><b>Description</b></td>
    <td valign="top" align="center"><b>Required</b></td>
  </tr>
  <tr>
    <td valign="top">class</td>
    <td valign="top">the fully-qualified name of the class (or classes,
      separated by commas)</td>
    <td align="center" valign="top">Yes</td>
  </tr>
  <tr>
    <td valign="top">outputFile</td>
    <td valign="top">concatenates the resulting header or source files for all the classes listed into this file</td>
    <td align="center" valign="middle" rowspan="2">Yes</td>
  </tr>
  <tr>
    <td valign="top">destdir</td>
    <td valign="top">sets the directory where javah saves the header files or the
      stub files.</td>
  </tr>
  <tr>
    <td valign="top">force</td>
    <td valign="top">specifies that output files should always be written (JDK1.2 only)</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">old</td>
    <td valign="top">specifies that old JDK1.0-style header files should be generated
      (otherwise output file contain JNI-style native method      function prototypes) (JDK1.2 only)</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">stubs</td>
    <td valign="top">generate C declarations from the Java object file (used with old)</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">verbose</td>
    <td valign="top">causes Javah to print a message concerning the status     of the generated files</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">classpath</td>
    <td valign="top">the classpath to use.</td>
    <td align="center" valign="top">No</td>
  </tr>
  <tr>
    <td valign="top">bootclasspath</td>
    <td valign="top">location of bootstrap class files.</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">extdirs</td>
    <td valign="top"> location of installed extensions.</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">implementation</td>
    <td valign="top">The compiler implementation to use.  If this
    attribute is not set, the default compiler for the current VM
    will be used.  (See the above <a
    href="#implementationvalues">list</a> of valid compilers.)</td>
    <td align="center" valign="top">No</td>
  </tr>
</table>
<p>Either outputFile or destdir must be supplied, but not both.&nbsp;</p>

<h3>Parameters specified as nested elements</h3>

<h4>arg</h4>

<p>You can specify additional command line arguments for the compiler
with nested <code>&lt;arg&gt;</code> elements.  These elements are
specified like <a href="../using.html#arg">Command-line Arguments</a>
but have an additional attribute that can be used to enable arguments
only if a given compiler implementation will be used.</p>

<table border="1" cellpadding="2" cellspacing="0">
<tr>
  <td width="12%" valign="top"><b>Attribute</b></td>
  <td width="78%" valign="top"><b>Description</b></td>
  <td width="10%" valign="top"><b>Required</b></td>
</tr>
  <tr>
    <td valign="top">value</td>
    <td align="center" rowspan="4">See
    <a href="../using.html#arg">Command-line Arguments</a>.</td>
    <td align="center" rowspan="4">Exactly one of these.</td>
  </tr>
  <tr>
    <td valign="top">line</td>
  </tr>
  <tr>
    <td valign="top">file</td>
  </tr>
  <tr>
    <td valign="top">path</td>
  </tr>
  <tr>
    <td valign="top">prefix</td>
    <td align="center" rowspan="2">See
    <a href="../using.html#arg">Command-line Arguments</a>.
    <em>Since Ant 1.8.</em></td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">suffix</td>
    <td valign="top" align="center">No</td>
  </tr>
  <tr>
    <td valign="top">implementation</td>
    <td>Only pass the specified argument if the chosen compiler
    implementation matches the value of this attribute.  Legal values
    are the same as those in the above <a
    href="#implementationvalues">list</a> of valid compilers.)</td>
    <td align="center">No</td>
  </tr>
</table>

<h4>implementationclasspath <em>since Ant 1.8.0</em></h4>

<p>A <a href="../using.html#path">PATH like structure</a> holding the
  classpath to use when loading the compiler implementation if a
  custom class has been specified.  Doesn't have any effect when
  using one of the built-in compilers.</p>

<h4>Any nested element of a type that implements JavahAdapter
  <em>since Ant 1.8.0</em></h4>

<p>If a defined type implements the <code>JavahAdapter</code>
  interface a nested element of that type can be used as an
  alternative to the <code>implementation</code> attribute.</p>

<h3>Examples</h3>
<pre>  &lt;javah destdir=&quot;c&quot; class=&quot;org.foo.bar.Wibble&quot;/&gt;</pre>
<p>makes a JNI header of the named class, using the JDK1.2 JNI model. Assuming
the directory 'c' already exists, the file <tt>org_foo_bar_Wibble.h</tt>
is created there. If this file already exists, it is left unchanged.</p>
<pre>  &lt;javah outputFile=&quot;wibble.h&quot;&gt;
    &lt;class name=&quot;org.foo.bar.Wibble,org.foo.bar.Bobble&quot;/&gt;
  &lt;/javah&gt;</pre>
<p>is similar to the previous example, except the output is written to a file
called <tt>wibble.h</tt>
in the current directory.</p>
<pre>  &lt;javah destdir=&quot;c&quot; force=&quot;yes&quot;&gt;
    &lt;class name=&quot;org.foo.bar.Wibble&quot;/&gt;
    &lt;class name=&quot;org.foo.bar.Bobble&quot;/&gt;
    &lt;class name=&quot;org.foo.bar.Tribble&quot;/&gt;
  &lt;/javah&gt;</pre>
<p>writes three header files, one for each of the classes named. Because the
force option is set, these header files are always written when the Javah task
is invoked, even if they already exist.</p>
<pre>  &lt;javah destdir=&quot;c&quot; verbose=&quot;yes&quot; old=&quot;yes&quot; force=&quot;yes&quot;&gt;
    &lt;class name=&quot;org.foo.bar.Wibble&quot;/&gt;
    &lt;class name=&quot;org.foo.bar.Bobble&quot;/&gt;
    &lt;class name=&quot;org.foo.bar.Tribble&quot;/&gt;
  &lt;/javah&gt;
  &lt;javah destdir=&quot;c&quot; verbose=&quot;yes&quot; stubs=&quot;yes&quot; old=&quot;yes&quot; force=&quot;yes&quot;&gt;
    &lt;class name=&quot;org.foo.bar.Wibble&quot;/&gt;
    &lt;class name=&quot;org.foo.bar.Bobble&quot;/&gt;
    &lt;class name=&quot;org.foo.bar.Tribble&quot;/&gt;
  &lt;/javah&gt;</pre>
<p>writes the headers for the three classes using the 'old' JNI format, then
writes the corresponding .c stubs. The verbose option will cause Javah to
describe its progress.</p>

<p>If you want to use a custom
  JavahAdapter <code>org.example.MyAdapter</code> you can either
  use the implementation attribute:</p>
<pre>
&lt;javah destdir="c" class="org.foo.bar.Wibble"
       implementation="org.example.MyAdapter"/&gt;
</pre>
<p>or a define a type and nest this into the task like in:</p>
<pre>
&lt;componentdef classname="org.example.MyAdapter"
              name="myadapter"/&gt;
&lt;javah destdir="c" class="org.foo.bar.Wibble"&gt;
  &lt;myadapter/&gt;
&lt;/javah&gt;
</pre>
<p>in which case your javah adapter can support attributes and
  nested elements of its own.</p>

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